One of the best and worst things about Advanced Dungeons & Dragons was the Monster Manual and the Fiend Folio. They provided hours of entertainment to my younger brother and me outside of role-playing. My brother's copy of the Monster Manual was our very first exposure to role-playing games years before we knew what a role-playing game was. If it was a book filled with illustrations of monsters, we were fascinated by it. Once we started role-playing, it was a double-edged sword. It was a useful and inspiring resource for me as a Dungeon Master, but for my players (and for me when I was a player) it was an unintentional source of cheating. Hours of poring through monster descriptions is bound to give players an advantage and spoil the surprise. Alas, as in most forms of fiction, the surprise is at least half the fun. Even the new monsters introduced in adventure modules were destined to reappear in the Monster Manual 2, which would be devoured by DMs and players alike. Some were lucky enough to encounter the monsters as players before the book was published, but as more and more players discovered the hobby, they were destined to have their surprises spoiled by the availability of published statistics.
When Dungeon Crawl Classics RPG was first published, it asserted the importance of monsters as an element of the unknown. They were to be the subject of rumors if they were known at all, and player characters would be encountering them with little to no prior knowledge. This preserved the spirit of adventure prevalent in sword & sorcery fiction (one of the main inspirations of DCC RPG), and it enabled many players to relive the thrill of fantasy role-playing when they were first introduced to it and everything was new. Only a few monsters were included in the rule book to be used as a benchmark for judges to create their own. It seemed that manuals of monsters were antithetical to the spirit of DCC RPG, and yet its publisher, Goodman Games, is running a Kickstarter project for just such a tome entitled Dungeon Denizens, and I have backed it. Why? Am I suddenly feeling the grip of Ye Olde Fear of Missing Out? It may be a bit of that, but I think the more pertinent reason is that, unlike D&D, DCC RPG has less clearly defined levels of challenge in regard to monsters. I need more of these benchmarks mentioned in the rule book to help guide me in creating foes for this system. Regardless of which monsters from Dungeon Denizens I decide to use in the adventures I design, I will keep in mind the excellent advice from Chapter 9 (of DCC RPG) under the heading "Keeping Monsters Mysterious."
So, go ahead and back the Dungeon Denizens Kickstarter project, but if you're playing in one of my games, expect the unexpected.